Intracerebral neural grafting has emerged as a possible new strategy for stimulation of regeneration and functional recovery in neurodegenerative diseases. While the emerging results of neural grafting in patients with Parkinson's disease are promising, it is clear that the transplantation approach needs further improvements. The mechanisms by which neural transplants induce their functional effects must be explored further and the overall efficacy of the transplantated cells must be increased. Efforts should also be made to find alternative sources of cells for transplantation based on, e.g., cell proliferation or genetic engineering techniques. The proposed work is focussed on 3 major research lines: (1) Studies on the functional regulation of grafted neurons, transplanted to the striatum or hippocampus in lesioned adult rats, using the microdialysis technique. (2) Studies on the functional role of afferent and efferent graft-host connections using cellular markers of neuronal activity combined with anterograde and retrograde neuroanatomical tracing. These experiments will focus, first, on the effects of dopamine released from intrastriatal grafts of fetal nigral tissue in animals with unilateral 6-OHDA lesions, and secondly, on the role of cortical and nigral afferents in the regulation of grafted fetal striatal neurons implanted into the ibotenic acid lesioned striatum. In a first step, we will use antibodies to the FOS protein, and oligonucleotide probes for mRNA of c-fos, enkephalin, substance P and GAD, as functional cellular markers. (3) Studies on the functional properties of primary cells and immortalized cell lines genetically engineered to produce L-DOPA (or dopamine), GABA and acetylcholine (ACh). These cells, which are produced by Dr. Horellou, Paris, will be implanted into the striatum or hippocampus in animals with dopamine-, GABA-, and ACh-depleting brain lesions. Their transmitter secretion will be studied in vivo by microdialysis, their functional effects will be followed in our standard behavioral tests for sensorimotor functions (DOPA- and GABA-producing cells), spatial learning (ACh cells) and kindling-induced epilepsy (GABA cells). Long-term survival, morphological features, and immunogenic properties will be studied by immunohistochemistry, and long-term expression of the inserted gene will be assessed with immunohistochemistry and in situ hybridization of their respective mRNAS:s. Comparison between implanted fetal neurons and genetically engineered cells in the same in vivo models should help to define the unnecessary requirements for functional recovery by transmitter- producing implants.